window.onload = function () {
  // 配置
  let config = {
    vx: 4, // 小球x轴速度,正为右，负为左
    vy: 4, // 小球y轴速度
    height: 2, // 小球高宽，其实为正方形，所以不宜太大
    width: 2,
    count: 200, // 点个数
    color: '121, 162, 185', // 点颜色
    stroke: '130,255,255', // 线条颜色
    dist: 6000, // 点吸附距离
    e_dist: 20000, // 鼠标吸附加速距离
    max_conn: 10 // 点到点最大连接数
  }

  // 调用
  CanvasParticle(config)
}
var CanvasParticle = (function () {
  // 根据传入的config初始化画布
  function canvasInit (canvasConfig) {
    canvasConfig = canvasConfig || {}
    // 获取body作为背景
    // var body = getElementByTag('body')[0]

    // 获取特定div作为背景
    // mydiv是你想要将其作为背景的div的ID
    var body = document.getElementById('app')
    var canvasObj = document.createElement('canvas')

    var canvas = {
      element: canvasObj,
      points: [],
      // 默认配置
      config: {
        vx: canvasConfig.vx || 4,
        vy: canvasConfig.vy || 4,
        height: canvasConfig.height || 2,
        width: canvasConfig.width || 2,
        count: canvasConfig.count || 100,
        color: canvasConfig.color || '121, 162, 185',
        stroke: canvasConfig.stroke || '130,255,255',
        dist: canvasConfig.dist || 6000,
        e_dist: canvasConfig.e_dist || 20000,
        max_conn: 10
      }
    }

    // 获取context
    if (canvas.element.getContext('2d')) {
      canvas.context = canvas.element.getContext('2d')
    } else {
      return null
    }

    body.style.padding = '0'
    body.style.margin = '0'
    // body.replaceChild(canvas.element, canvasDiv);
    body.appendChild(canvas.element)

    canvas.element.style = 'position: fixed; top: 0; left: 0; z-index: -1'
    canvasSize(canvas.element)
    window.onresize = function () {
      canvasSize(canvas.element)
    }
    body.onmousemove = function (e) {
      var event = e || window.event
      canvas.mouse = {
        x: event.clientX,
        y: event.clientY
      }
    }
    document.onmouseleave = function () {
      canvas.mouse = undefined
    }
    setInterval(function () {
      drawPoint(canvas)
    }, 40)
  }

  // 设置canvas大小
  function canvasSize (canvas) {
    // 获取窗口的宽高
    // canvas.width = window.innerWeight || document.documentElement.clientWidth || document.body.clientWidth;
    // canvas.height = window.innerWeight || document.documentElement.clientHeight || document.body.clientHeight;

    // 获取特定div的宽高
    var width = document.getElementById('app').style.width
    var height = document.getElementById('app').style.height
    width = parseInt(width)
    height = parseInt(height)
    canvas.width = width || window.innerWeight || document.documentElement.clientWidth || document.body.clientWidth
    canvas.height = height || window.innerWeight || document.documentElement.clientHeight || document.body.clientHeight
  }

  // 画点
  function drawPoint (canvas) {
    let context = canvas.context
    let point
    context.clearRect(0, 0, canvas.element.width, canvas.element.height)
    context.beginPath()
    context.fillStyle = 'rgb(' + canvas.config.color + ')'
    for (var i = 0, len = canvas.config.count; i < len; i++) {
      if (canvas.points.length !== canvas.config.count) {
        // 初始化所有点
        point = {
          x: Math.floor(Math.random() * canvas.element.width),
          y: Math.floor(Math.random() * canvas.element.height),
          vx: canvas.config.vx / 2 - Math.random() * canvas.config.vx,
          vy: canvas.config.vy / 2 - Math.random() * canvas.config.vy
        }
      } else {
        // 处理球的速度和位置，并且做边界处理
        point = borderPoint(canvas.points[i], canvas)
      }
      context.fillRect(point.x - canvas.config.width / 2, point.y - canvas.config.height / 2, canvas.config.width, canvas.config.height)

      canvas.points[i] = point
    }
    drawLine(context, canvas, canvas.mouse)
    context.closePath()
  }

  // 边界处理
  function borderPoint (point, canvas) {
    var p = point
    if (point.x <= 0 || point.x >= canvas.element.width) {
      p.vx = -p.vx
      p.x += p.vx
    } else if (point.y <= 0 || point.y >= canvas.element.height) {
      p.vy = -p.vy
      p.y += p.vy
    } else {
      p = {
        x: p.x + p.vx,
        y: p.y + p.vy,
        vx: p.vx,
        vy: p.vy
      }
    }
    return p
  }

  // 画线
  function drawLine (context, canvas, mouse) {
    context = context || canvas.context
    for (var i = 0, len = canvas.config.count; i < len; i++) {
      // 初始化最大连接数
      canvas.points[i].max_conn = 0
      // point to point
      let dist
      for (var j = 0; j < len; j++) {
        if (i !== j) {
          dist = Math.round(canvas.points[i].x - canvas.points[j].x) * Math.round(canvas.points[i].x - canvas.points[j].x) +
            Math.round(canvas.points[i].y - canvas.points[j].y) * Math.round(canvas.points[i].y - canvas.points[j].y)
          // 两点距离小于吸附距离，而且小于最大连接数，则画线
          if (dist <= canvas.config.dist && canvas.points[i].max_conn < canvas.config.max_conn) {
            canvas.points[i].max_conn++
            // 距离越远，线条越细，而且越透明
            context.lineWidth = 0.5 - dist / canvas.config.dist
            context.strokeStyle = 'rgba(' + canvas.config.stroke + ',' + (1 - dist / canvas.config.dist) + ')'
            context.beginPath()
            context.moveTo(canvas.points[i].x, canvas.points[i].y)
            context.lineTo(canvas.points[j].x, canvas.points[j].y)
            context.stroke()
          }
        }
      }
      // 如果鼠标进入画布
      // point to mouse
      if (mouse) {
        dist = Math.round(canvas.points[i].x - mouse.x) * Math.round(canvas.points[i].x - mouse.x) +
          Math.round(canvas.points[i].y - mouse.y) * Math.round(canvas.points[i].y - mouse.y)
        // 遇到鼠标吸附距离时加速，直接改变point的x，y值达到加速效果
        if (dist > canvas.config.dist && dist <= canvas.config.e_dist) {
          canvas.points[i].x = canvas.points[i].x + (mouse.x - canvas.points[i].x) / 20
          canvas.points[i].y = canvas.points[i].y + (mouse.y - canvas.points[i].y) / 20
        }
        if (dist <= canvas.config.e_dist) {
          context.lineWidth = 1
          context.strokeStyle = 'rgba(' + canvas.config.stroke + ',' + (1 - dist / canvas.config.e_dist) + ')'
          context.beginPath()
          context.moveTo(canvas.points[i].x, canvas.points[i].y)
          context.lineTo(mouse.x, mouse.y)
          context.stroke()
        }
      }
    }
  }
  return canvasInit
})()
